Tuning the Photophysical Properties of Push-Pull Azaheterocyclic Chromophores by Protonation: A Brief Overview of a French-Spanish-Czech Project

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Tuning the Photophysical Properties of Push-Pull Azaheterocyclic Chromophores by Protonation: A Brief

Overview of a French-Spanish-Czech Project

Sylvain Achelle, Julián Rodríguez-López, Filip Bureš, Françoise Robin-Le Guen

To cite this version:

Sylvain Achelle, Julián Rodríguez-López, Filip Bureš, Françoise Robin-Le Guen. Tuning the Photo- physical Properties of Push-Pull Azaheterocyclic Chromophores by Protonation: A Brief Overview of a French-Spanish-Czech Project. Chemical Record, Chemical Society of Japan, 2020, 20 (5), pp.440-451.

�10.1002/tcr.201900064�. �hal-02364874�

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Tuning the Photophysical Properties of Push-Pull Azaheterocyclic Chromophores by Protonation: A Brief Overview of a French- Spanish-Czech Project

Sylvain Achelle,*

Julián Rodríguez-López,*

Filip Bureš,

and Françoise Robin-le Guen

[a]

Université de Rennes, CNRS, Institut des Sciences Chimiques de Rennes - UMR 6226, F 35000 Rennes, France; E-mail: [email protected]

[b]

Área de Química Orgánica, Facultad de Ciencias y Tecnologías Químicas, Universidad de Castilla-La Mancha, Avda. Camillo José Cela 10, 13071 Ciudad Real, Spain; E-mail:

[email protected]

[c]

Institute of Organic Chemistry and Technology, Faculty of Chemical Technology, University of Pardubice, Studenská 573, Pardubice 53210, Czech Republic.

Graphical abstract

An account is provided of our studies on the effect that the addition of acid has on the

photophysical properties of π-extended push-pull chromophores that incorporate

azaheterocyclic rings as electron-withdrawing moieties. The work carried out to afford white

light-emitting materials based on an equilibrium between neutral and protonated forms that

emit complementary colors is described.

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Biographical sketches

Sylvain Achelle received his PhD in organic chemistry in 2007 from INSA Rouen (France).

After two post-doctoral stays at the Universidad de Castilla-La Mancha (Spain) and Institut Curie (France), he was recruited as associate professor at IUT Lannion, University of Rennes 1, in 2010. He obtained the habilitation to direct research in 2014. His main research topics include the luminescence and nonlinear optical properties of organic and organometallic heterocyclic derivatives. He has published 60 scientific articles (h-index: 23 according to Web of Science) and he is currently associate editor of the journal Dyes & Pigments.

Julián Rodríguez López studied chemistry at the Universidad Complutense de Madrid

(UCM) and obtained his PhD with honors (cum laude) in 1990. He was a Fulbright

postdoctoral fellow at the University of Texas at Austin for one year, under the supervision of

Professor Philip Magnus. After successive positions at the UCM, he joined the Universidad de

Castilla-La Mancha at Ciudad Real in 1995, where he is currently full professor in organic

chemistry. His research concerns the synthesis and photophysical properties of novel π-

conjugated systems, especially dendrimers and diazine derivatives.

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Filip Bureš studied chemistry at the University of Pardubice, where he also obtained his PhD in organic chemistry in 2005. He pursued (post)doctoral studies with Professor P. Knochel (LMU, Munich) and Professor F. Diederich (ETH, Zurich). In 2007 he established a working group at the Institute of Organic Chemistry, University of Pardubice, which focuses on the design and synthesis of π-conjugated molecules for miscellaneous (opto)electronic applications.

Françoise Robin-le Guen received her PhD in organometallic chemistry from the University

of Bretagne Occidentale (France). She is currently full professor at IUT Lannion, University

of Rennes 1 and head of the heterocyclic organometallic teams at the Chemical Sciences

Institute of Rennes. Her main research topics are focused on the design of π-conjugated

heterocyclic and organometallic systems for dye-sensitized solar cells, luminescence and

nonlinear optics.

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Abstract: Conjugated push-pull molecules that incorporate nitrogen heterocycles as electron- withdrawing units are interesting materials because of their luminescence properties. These chromophores can be easily and reversibly protonated at the nitrogen atom of the heterocyclic ring and this can cause dramatic color changes. White and multi-color photoluminescence both in solution and in the solid state can be obtained by an accurate control of the amount of acid. Thus, with a suitable design these compounds have potential applications in the development of colorimetric pH sensors and the fabrication of OLEDs based on only one material. We provide here a brief overview of our collaborative efforts made in this area.

Keywords: white-light emission, push-pull chromophores, nitrogen heterocycles, protonation, photoluminescence.

Introduction

The design of push-pull chromophores has been the subject of intensive research

during the past few decades.

In this context, π-deficient nitrogen heterocycles such as

pyridine,

quinoline,

diazines (pyridazine,

pyrimidine,

and pyrazine

), benzodiazines

(quinoxaline,

3

6

quinazoline,

3

5

phthalazine,

etc.), phenanthroline,

triazines,

and

tetrazines

are considered as moderate-to-strong electron withdrawing groups. Some push-

pull chromophores that bear these heterocycles as the electron-attracting part exhibit intense

luminescence properties. In such cases an intramolecular charge transfer (ICT) occurs and this

can be easily tuned by adjusting the donor/attractor couple, the π-conjugated linker or by

developing multipolar structures.

1

An enhanced ICT leads to a bathochromic effect on the

absorption spectrum whereas the effect on the emission becomes less predictable: either an

increase or decrease in the intensity accompanied by a red shift, along with total quenching,

can be observed depending on the structure. Engaging the electron lone pair of the nitrogen

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atoms of azaheterocycles provides a way to increase their electron-withdrawing character. In this respect, it is feasible to induce substantial changes in the photophysical properties of push-pull molecules bearing such fragments by complexation,

alkylation,

or reversible protonation.

This latter case is called halochromism or acidochromism. The general mechanism for the halochromic response is the redistribution of the charge density due to protonation, which promotes changes in the electronic structure. As a consequence, azaheterocyclic chromophores can be used as pH sensors.

Likewise, a series of pyridine- based molecules were reported to be acid-triggered reversible luminescent and nonlinear optical (NLO) switches both in solution and in the solid state.

The linear and NLO properties could also be tuned by coordination to metal centers.

Moreover, tuning of the photo- and electroluminescence was achieved by an in situ controlled non-reversible thermal deprotonation, which can be exploited to fabricate smart thermal sensors and antifraud devices.

The controlled protonation of some blue-emitting azaheterocyclic derivatives affords white photo- and electroluminescence by the formation of orange-emissive acidified species.

Over the past few decades our groups have intensively studied the photophysical properties of push-pull chromophores based on nitrogen heterocycles. In particular, we recently focused our investigations on the structure-dependent effect of protonation on the luminescence properties of such chromophores. One of our goals was to obtain efficient white light-emitting materials based on neutral and protonated forms that emit complementary colors. In this personal account, we would like to provide a brief overview of our ‘French- Spanish-Czech’ collaborative efforts made in this direction.

Pyrimidine chromophores

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The pyrimidine nucleus generally acts as a monobasic compound with pK

≈ 1.1.

Thus, it is a weaker base than pyridine (pK

≈ 5.2). Protonation of the first nitrogen atom leads to a marked decrease in the basicity of the second nitrogen atom due to the attractive inductive effect of the resulting quaternary nitrogen (second pK

≈ –6.3).

Although some of us described some basic information on the pH sensitivity of

arylpyrimidine derivatives in 2008,

the first comprehensive study on the effects of the

protonation concerns 4,6-bis(arylvinyl)pyrimidines 1–8 (Figure 1).

With the exception of

compound 3, which has a trifluoromethyl electron-withdrawing substituent, the addition of

trifluoroacetic acid (TFA) to a CH

Cl

solution of compounds 1–8 induced a dramatic color

change (Figure 1). This color change was fully reversible by neutralization with a base such

as Et

N or KBu

O. As far as emission is concerned, compounds substituted with moderate

electron-donating groups (1, 4, 5 and 7) or CF

fragments (3) remained luminescent upon

protonation and this was associated with a red-shifted emission band, a significant decrease in

the Stokes shifts and, in some cases, an increase in the fluorescence quantum yield (1, 3 and

4). For stronger electron-donating groups such as NPh

(chromophore 2) and for the dendritic

structure 8, the emission was completely quenched after protonation, whereas ferrocene

derivative 6 remained non-emissive in acidic media. Similarly, an acetonitrile solution of the

arylvinylpyrimidine 9, which contains a dipicolylamine substituent, showed red-shifted

absorption and emission quenching upon addition of TFA (Figure 1).

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Figure 1. Color change of CH

Cl

solutions of compounds 1–8 (acetonitrile solution for 9) after treatment with TFA.

4-Arylvinyl-2,6-di(pyridin-2-yl)pyrimidines

10, 11, 13 and 14, 4- arylvinylpyrimidines 15–17, 19–22, 24, 27 and 28, and 2-arylvinylpyrimidines 29–33 (Figure 2)

exhibited similar behavior to that found for 4,6-bis(arylvinyl)pyrimidine

derivatives 1–8. Namely, THF or CH

Cl

solutions of these compounds underwent a

significant color change upon addition of acid (Figure 3). Whereas a red shift of the charge

transfer absorption band was observed, the emission was either completely quenched for the

compounds substituted with strong electron-donating amino groups (11, 14, 16, 17, and 24) or

red-shifted for chromophores with weaker methyl, methoxy, and thiomethyl electron donors

(10, 13, 15, 19, 21, and 22). As an example, the change in the absorption and emission spectra

of a THF solution of 10 upon gradual addition of p-toluensulfonic acid (p-TSA) is shown in

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Figure 4. Compound 20 remained non-emissive upon protonation. Theoretical calculations performed on compound 19 indicated that planarization of the structure occurs upon protonation along with reduction of the bond length alternation (BLA) value in the vinyl unit.

The most favorable site for protonation in the ground state was found at N1. It should be noted that for dimethylamino derivatives 12 and 23, as well as piperidinyl compounds 18 and 25, the protonation led to a blue-shifted absorption due to protonation of the basic amino groups. Nevertheless, this phenomenon was not observed for 2-arylvinylpyrimidines 31 and 33.

Surprisingly, in contrast to monosubstituted triphenylamine 16 and 2,6-di(pyridin-2- yl)pyrimidine analog 14, the protonated form of 26 remained luminescent in CH

Cl

with an emission band at 570 nm.

This fact can be explained by a slightly reduced ICT in this case.

Color change and protonation for compounds 27 and 28, with an extended π -conjugated linker, was observed at higher concentrations of TFA (10

–10

M) than for other diazine derivatives with shorter π-conjugated scaffolds.

Figure 2. Chemical structures of compounds 10–33.

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Figure 3. Color change of CH

Cl

solutions of compounds 16, 20, and 17 (from left to right) (c = 10

M in the presence of 10

M TFA). Adapted with permission from reference [24]

(copyright 2012 American Chemical Society).

Figure 4. Changes in the absorption (left) and emission (right) spectra of 10 (2.0 × 10

M in THF) upon addition of p-TSA (7.5 × 10

M to a large excess). Reproduced with permission from reference [23] (copyright 2011 American Chemical Society).

4-Arylvinylpyrimidine chromophores have also been incorporated into polymethyl

methacrylate-based copolymers 34–36 (Figure 5).

The macromolecules displayed similar

photophysical properties in CH

Cl

solution when compared to the free chromophores. Thus,

upon adding acid, a red shift was obtained both in the absorption and emission spectra. The

emission was partially (34) or totally (35) quenched for the amino-substituted compounds.

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Figure 5. Chemical structures of copolymers 34–36.

The behavior upon acidic treatment of pyranylidene derivatives 37–39 (Figure 6) depends on the π-conjugated linker. The addition of acid to compounds 37 and 38 led to a significant red shift in the absorption and this is attributed to protonation of the pyrimidine ring, with the solution remaining non-emissive.

Compound 39, with a phenylene unit in the linker, showed different behavior: a blue-shifted absorption band appeared progressively upon addition of TFA and the protonated species exhibited an intense blue emission at 450 nm (Φ

= 0.13) attributed to the formation of a pyrylium cation.

Figure 6. Chemical structures of pyranylidenes 37–39.

Chromophores 11 (Figure 2) and 40 (Figure 7) have been incorporated into pluronic

F68 nanoparticles and stable aqueous colloidal solutions were obtained.

The position of the

absorption band of the aqueous emulsions was virtually the same as that of the chloroform

solutions. On decreasing the pH, these emulsions underwent an immediate and fully

reversible color change from yellow to purple. The spectra showed the decrease of the initial

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band located at around 420 nm for both chromophores, together with the development of a new red-shifted band located at 480 nm for 11 and 530 nm for 40 (Figure 7). The pK

values were estimated to be 1.1 and 1.8 for 11 and 40, respectively. The ‘pH switch’ value between the yellow and purple forms is very low, but these nanoparticle assemblies behave as colorimetric pH sensors in aqueous media. It should be noted that all aqueous emulsions were non-emissive – probably due to hydrogen bonding interactions between the hydrophilic pluronic segments and/or water protons with the nitrogen atoms of the pyrimidine ring.

Figure 7. Absorption spectra of dilute pluronic F-68 nanoparticles incorporating chromophore 40 at acidic, basic and intermediate pH (dotted line). Inset: color change upon addition of HCl. Adapted with permission from reference [31] (copyright 2012 Springer).

The change in the color emission of a CH

Cl

solution of the tristyrylpyrimidine 41

upon addition of (1S)-(+)-10-camphorsulfonic acid (CSA) is illustrated in Figure 8.

The

photoluminescence spectra are characterized by the progressive disappearance of the band of

the neutral form at 441 nm, which is accompanied by the progressive appearance of a new

red-shifted band at 540 nm that corresponds to the monoprotonated species. The neutral form

emits dark blue light whereas the protonated form emits green light. A mixture of the two

produces cyan light.

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Figure 8. Left: changes in the emission spectra of a CH

Cl

solution of 41 (c = 9.64 × 10

M) upon addition of CSA (0.1–50 equiv). λ

= 380 nm. Right: changes in the color after addition of 0.8 equiv (middle) and 50 equiv of CSA (right). The pictures were taken in the dark upon irradiation with a hand-held UV lamp (λ

= 366 nm). Adapted with permission from reference [32] (copyright 2018 American Chemical Society).

As previously shown, the emission of amino-substituted pyrimidines is generally (partially) quenched upon protonation. Nevertheless, the presence of weaker electron- donating groups occasionally results in a moderate quenching or even an enhancement of the fluorescence intensity. The fluorescence quantum yields of these compounds are mostly low, but the extension of the π-conjugated scaffold leads to a significant enhancement of the

fluorescence intensity without modifying the solubility properties of the chromophores. Blue

emitting neutral forms can be combined with red/orange protonated species to obtain white

emitting materials. With this goal, a series of seven methoxy-substituted pyrimidine

derivatives 5 (Figure 1), 19 (Figure 2), and 42–46 (Figure 9) with extended π-conjugated

backbones was studied.

In CH

Cl

solution, compound 19 and thiophene derivatives 43

and 45 exhibited low emission quantum yields (Φ

< 0.04). Nevertheless, compounds 5, 42,

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44, and 46 are highly emissive in both the neutral (Φ

< 0.14–0.90) and protonated forms (Φ

< 0.15–0.72). The color changes of CH

Cl

solutions of 42 and 44 upon gradual addition of TFA are shown in Figure 10. White light emission was observed with chromaticity coordinates of (0.32, 0.36) for 42 with 20 equivalents of TFA (λ

= 346 nm) and (0.33, 0.33) for 44 with 100 equivalents of TFA (λ

= 355 nm). Fluorophore 5 also exhibited white photoluminescence by controlled protonation both in solution and the solid state when incorporated into a polymer matrix.

The emission spectra and the color changes of thin films of polystyrene doped with 1 wt% of 5 in the absence and the presence of TFA, respectively, are shown in Figure 11.

Figure 9. Chemical structures of methoxy derivatives 42–46.

Figure 10. a) Changes in the color of a solution of 42 (c = 1.6 × 10

M in CH

Cl

, left) after addition of 10 equivalents (middle) and 1000 equivalents (right) of TFA. b) Changes in the color of a solution of 44 (c = 1.2 × 10

M in CH

Cl

, left) after addition of 100 equivalents (middle) and 1000 equivalents (right) of TFA. Photographs were taken upon irradiation with a hand-held UV-lamp (λ

= 366 nm). Reproduced with permission from reference [25]

(copyright 2016 American Chemical Society).

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Figure 11. Emission spectra of a polystyrene thin film doped with 1 wt% of 5 in the absence (blue) and the presence (red, 50 equivalents) of TFA. Inset: Color of the films in the absence (left) and the presence of 50 equivalents (middle) and 1000 equivalents (right) of TFA.

Photographs were taken upon irradiation with a hand-held UV-lamp (λ

= 366 nm). Adapted with permission from reference [33] (copyright 2015 Royal Chemical Society).

A series of carbazole- and triphenylamine-substituted pyrimidines 47–52 (Figure 12)

was also designed for white light emission.

In this case, the shortening of the π-conjugated

scaffold is compensated by the stronger electron-donating character of the carbazolyl and

diphenylamino groups with respect to the methoxy group. All of these compounds exhibited

an intense purple/blue luminescence in CH

Cl

solution with high fluorescence quantum

yields (up to 0.86 for 49). Triphenylamine derivatives 47, 49, and 51 as well as 2-carbazolyl

pyrimidine 48 showed almost no luminescence upon addition of camphorsulfonic acid,

although 50 and 52 led to intense yellow luminescence under the same conditions (Φ

= 0.63

for 50 and Φ

= 0.45 for 52). White light emission both in solution and in solid state was

observed by a combination of neutral and protonated forms of 52 (Figure 13).

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Figure 12. Chemical structures of compounds 47–52.

Figure 13. Top: Changes in the color of a solution of 52 (c = 1.25 × 10

M in CH

Cl

, left)

after addition of 45 equivalents (middle) and in 10

M CSA (right). Bottom: Changes in the

color of filter paper samples after immersion in a CH

Cl

solution of polystyrene doped with

52 (1 wt%) in the absence (left) and presence of 0.1 equivalents (middle) and 80 equivalents

(right) of camphorsulfonic acid. Photographs were taken upon irradiation with a hand-held

UV-lamp (λ

= 366 nm).

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Other diazine and benzodiazine chromophores

Other diazines such as pyrazine (pK

≈ 0.65) and pyridazine (pK

≈ 2.3) and benzodiazines such as quinoxaline (pK

≈ 0.56) and quinazoline (pK

≈ 3.5) are also monobases that can be protonated.

Compounds 53–55 (Figure 14) were compared to their pyrimidine analog 19 (Figure 2).

All compounds displayed red-shifted absorption upon protonation by TFA. As far as the emission was concerned, the effect of protonation varied according to the nature of the diazine ring. Whereas the progressive addition of acid prompted a color change from blue to green in the emission of pyrimidine 19, the luminescence of pyrazine 54 and quinoxaline 55 was attenuated and ultimately quenched, as illustrated in Figure 15 for a CH

Cl

solution of compound 54. In contrast, pyridazine 53 was not luminescent and remained non-emissive after protonation. Theoretical calculations predicted that protonation was favored on the nitrogen atom farthest from the vinyl moiety. The protonated pyridazine derivative 53 remained non-fluorescent because vanishing overlap occurs between the HOMO located on the methoxynaphthylvinyl moiety and the LUMO centered on the diazine ring. For pyrazine and quinoxaline derivatives 54 and 55, the emission was computed to be considerably red- shifted to the near IR region where nonradiative decays are well known to be more efficient.

Moreover, given that the bright excited state for quinoxaline 55 in the gas phase was

envisaged to be destabilized by more than 11 kcal/mol, such nonradiative channels probably

explain the fluorescence quenching of this protonated quinoxaline derivative. Nevertheless,

some quinoxaline chromophores exhibit a more intense and red-shifted emission after

protonation.

On the other hand, dimethylamino derivatives 56–58 (Figure 14) displayed

blue-shifted absorption due to the protonation of the amino group.

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Figure 14. Chemical structures of compounds 53–58.

Figure 15. Changes in the emission spectra of a CH

Cl

solution of 54 upon addition of TFA (10–30000 equiv), λ

= 352 nm. Reproduced with permission from reference [25] (copyright 2016 American Chemical Society).

The effect of protonation on the photophysical properties of a series of amino-

substituted quinazoline chromophores 59–63 (Figure 16) has been also studied.

In all

cases, a red-shifted absorption, as evidenced by the significant color change experienced by

their CH

Cl

solutions (Figure 17), associated with total emission quenching was observed. It

would be interesting to study the effect of protonation with other quinazolines substituted by

weaker electron-donating fragments, such as methoxy or carbazolyl groups.

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Figure 16. Chemical structures of compounds 59–63.

Figure 17. Color change of CH

Cl

solutions of several quinazoline derivatives in the presence of TFA. Adapted with permission from reference [35] (copyright 2014 American Chemical Society).

Pyridine chromophores

Pyridine (pK

≈ 5.2) is a stro nger base than (benzo)diazines. The use of this basic

heterocyclic compound allows easy control of the acid-base equilibrium with the aim of

obtaining white luminescence. As the pyridine ring has a weaker electron-withdrawing

character than pyrimidine, the methoxy or carbazole substituents were replaced by stronger

electron-donating triphenylamino groups. Thus, a series of triphenylamine derivatives bearing

pyridine units 64–70 was designed (Figure 18).

Likewise, the corresponding

trifluoroacetate salts were isolated and characterized. For all series of compounds, the gradual

addition of TFA to CHCl

solutions led to the progressive disappearance of both of the

absorption and emission bands and the appearance of a new red-shifted absorption/emission

band. As an example, the changes for compound 70 are represented in Figure 19. Time-

resolved emission studies performed on compounds 67–69 revealed an energy transfer from

the neutral to the protonated species on the 1 ps time scale.

As expected, a substantial

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increase in the positive emission solvatochromic behavior for 64 was observed when protonated, which is consistent with a significant enhancement of the ICT in the acidified form. For all compounds, the controlled protonation of the blue emitting pyridine derivatives led to white photoluminescence in solution due to the formation of yellow/orange emissive pyridinium species (Figure 20, top). The chromaticity coordinates were close to those of pure white light (0.33, 0.33). Doped polystyrene thin films of compounds 64 and 70 were also prepared using different ratios of neutral and protonated forms. Unfortunately, although the films remained luminescent, it was not possible to obtain white light in the solid state. When compound 64 was used both the absorption and the emission band experienced a significant blue shift with regard to the CHCl

solution, and the chromaticity coordinates were far from those of pure white light. Multi-color photoluminescence was achieved by tuning the ratio of the pyridine/pyridinium forms in the case of fluorophore 70 (Figure 20, bottom).

Figure 18. Chemical structures of pyridine derivatives 64–70.

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Figure 19. Changes in the absorption (left) and emission spectra (right) of a CHCl

solution of 70 (c = 1.86 × 10

M) upon addition of TFA (0.1–5.0 equivalents). Reproduced with permission from reference [36] (copyright 2017 Elsevier).

Figure 20. Top: changes in the color of a CHCl

solution of 70 (c = 1.86 × 10

M) after the addition of 0.8 equivalents (middle) and 5 equivalents of TFA (right). Bottom: colors of polystyrene thin films of 70 (1 wt%) in the absence and the presence of 0.4, 0.6, and 5 equivalents of TFA (from left to right). Photographs were taken upon irradiation with a hand- held UV-lamp (λ

= 366 nm). Adapted with permission from reference [36] (copyright 2017 Elsevier).

In order to overcome this problem, the reinforcement of the electron-donating character of the triphenylamine was tested by the introduction of methoxy, carbazolyl or methoxythienyl fragments at the triphenylamine core (compounds 71–76, Figure 21).

Unfortunately, the protonated forms of these chromophores were not emissive in any case.

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Figure 21. Chemical structures of compounds 71–76.

Conclusions

The extraordinary optical properties of π-extended push-pull molecules that incorporate azaheterocyclic rings as electron-withdrawing moieties provide an important tool to develop new sensing and luminescent materials. In the last year, we have prepared and studied a large library of such chromophores through a fruitful collaborative ‘French-Spanish- Czech’ project. In this review we have illustrated the effect that the addition of acid has on the photophysical properties of these materials. White light photoluminescence can be obtained by controlled protonation, which involves an equilibrium between two different forms of complementary emitting colors. Nevertheless, major efforts are still required to harness the full potential of these compounds.

Acknowledgments

The authors wish to thank all those individuals who have been involved in the

different stages of the work described in the manuscript. Funding by the Junta de

Comunidades de Castilla-La Mancha/FEDER (project SBPLY/17/180501/000214) and the

Ministerio de Economía y Competitividad/Agencia Estatal de Investigación/FEDER (project

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European Regional Development Fund-Project "Organic redox couple based batteries for energetics of traditional and renewable resources (ORGBAT)" No.

CZ.02.1.01/0.0/0.0/16_025/0007445.

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